Folia are a rare formation found near or just below the water line. Found on celings and walls, they resemble inverted rimstone dams. They are thought to form primarily near the top of the water table, and are associated with a declining water level. Like shelfstone, they probably form from precipitates on water surfaces that accrete to walls. As the water lowers, more calcite is deposited underneath, forming a flat surface. Another theory suggests that carbon dioxide is trapped in the ribs and promotes calcite deposition inside.